func-names
Require or disallow named function expressions
A pattern that’s becoming more common is to give function expressions names to aid in debugging. For example:
Foo.prototype.bar = function bar() {};
Adding the second bar in the above example is optional. If you leave off the function name then when the function throws an exception you are likely to get something similar to anonymous function in the stack trace. If you provide the optional name for a function expression then you will get the name of the function expression in the stack trace.
Rule Details
This rule can enforce or disallow the use of named function expressions.
Options
This rule has a string option:
"always"(default) requires function expressions to have a name"as-needed"requires function expressions to have a name, if the name isn’t assigned automatically per the ECMAScript specification."never"disallows named function expressions, except in recursive functions, where a name is needed
This rule has an object option:
"generators": "always" | "as-needed" | "never""always"require named generators"as-needed"require named generators if the name isn’t assigned automatically per the ECMAScript specification."never"disallow named generators where possible.
When a value for generators is not provided the behavior for generator functions falls back to the base option.
Please note that "always" and "as-needed" require function expressions and function declarations in export default declarations to have a name.
always
Examples of incorrect code for this rule with the default "always" option:
Open in Playground
/*eslint func-names: ["error", "always"]*/
Foo.prototype.bar = () {};
const cat = {
() {}
}
(() {
// ...
}())
export default () {}
Examples of correct code for this rule with the default "always" option:
Open in Playground
/*eslint func-names: ["error", "always"]*/
Foo.prototype.bar = function bar() {};
const cat = {
meow() {}
}
(function bar() {
// ...
}())
export default function foo() {}
as-needed
ECMAScript 6 introduced a name property on all functions. The value of name is determined by evaluating the code around the function to see if a name can be inferred. For example, a function assigned to a variable will automatically have a name property equal to the name of the variable. The value of name is then used in stack traces for easier debugging.
Examples of incorrect code for this rule with the "as-needed" option:
Open in Playground
/*eslint func-names: ["error", "as-needed"]*/
Foo.prototype.bar = () {};
(() {
// ...
}())
export default () {}
Examples of correct code for this rule with the "as-needed" option:
Open in Playground
/*eslint func-names: ["error", "as-needed"]*/
var bar = function() {};
const cat = {
meow: function() {}
}
class C {
#bar = function() {};
baz = function() {};
}
quux ??= function() {};
(function bar() {
// ...
}())
export default function foo() {}
never
Examples of incorrect code for this rule with the "never" option:
Open in Playground
/*eslint func-names: ["error", "never"]*/
Foo.prototype.bar = () {};
(() {
// ...
}())
Examples of correct code for this rule with the "never" option:
Open in Playground
/*eslint func-names: ["error", "never"]*/
Foo.prototype.bar = function() {};
(function() {
// ...
}())
generators
Examples of incorrect code for this rule with the "always", { "generators": "as-needed" } options:
Open in Playground
/*eslint func-names: ["error", "always", { "generators": "as-needed" }]*/
(() {
// ...
}())
Examples of correct code for this rule with the "always", { "generators": "as-needed" } options:
Open in Playground
/*eslint func-names: ["error", "always", { "generators": "as-needed" }]*/
var foo = function*() {};
Examples of incorrect code for this rule with the "always", { "generators": "never" } options:
Open in Playground
/*eslint func-names: ["error", "always", { "generators": "never" }]*/
var foo = bar(() {});
Examples of correct code for this rule with the "always", { "generators": "never" } options:
Open in Playground
/*eslint func-names: ["error", "always", { "generators": "never" }]*/
var foo = bar(function *() {});
Examples of incorrect code for this rule with the "as-needed", { "generators": "never" } options:
Open in Playground
/*eslint func-names: ["error", "as-needed", { "generators": "never" }]*/
var foo = bar(() {});
Examples of correct code for this rule with the "as-needed", { "generators": "never" } options:
Open in Playground
/*eslint func-names: ["error", "as-needed", { "generators": "never" }]*/
var foo = bar(function *() {});
Examples of incorrect code for this rule with the "never", { "generators": "always" } options:
Open in Playground
/*eslint func-names: ["error", "never", { "generators": "always" }]*/
var foo = bar(() {});
Examples of correct code for this rule with the "never", { "generators": "always" } options:
Open in Playground
/*eslint func-names: ["error", "never", { "generators": "always" }]*/
var foo = bar(function *baz() {});
Compatibility
- JSCS: requireAnonymousFunctions
- JSCS: disallowAnonymousFunctions
Version
This rule was introduced in ESLint v0.4.0.
Further Reading
